Basic Electricity Notes

Transcription

1 Basic Electricity Notes EVERYTHING IS MADE OF ATOMS Imagine a pure gold ring. Divide it in half and give one of the halves away. Keep dividing and dividing and dividing. Soon you will have a piece so small you will not be able to see it without a microscope. It may be very, very small, but it is still a piece of gold. If you could keep dividing it into smaller and smaller pieces, you would finally get to the smallest piece of gold possible. It is called an atom. If you divided it into smaller pieces, it would no longer be gold. Everything around us is made of atoms. Scientists so far have found only 115 different kinds of atoms. Everything you see is made of different combinations of these atoms. PARTS OF AN ATOM So what are atoms made of? In the middle of each atom is a "nucleus." The nucleus contains two kinds of tiny particles, called protons and neutrons. Orbiting around the nucleus are even smaller particles called electrons. The 115 kinds of atoms are different from each other because they have different numbers of protons, neutrons and electrons. It is useful to think of a model of the atom as similar to the solar system. The nucleus is in the center of the atom, like the sun in the center of the solar system. The electrons orbit around the nucleus like the planets around the sun. Just like in the solar system, the nucleus is large compared to the electrons. The atom is mostly empty space. And the

2 electrons are very far away from the nucleus. While this model is not completely accurate, we can use it to help us understand static electricity. (Note: A more accurate model would show the electrons moving in 3- dimensional volumes with different shapes, called orbitals. This may be discussed in a future issue.) ELECTRICAL CHARGES Protons, neutrons and electrons are very different from each other. They have their own properties, or characteristics. One of these properties is called an electrical charge. Protons have what we call a "positive" (+) charge. Electrons have a "negative" (-) charge. Neutrons have no charge, they are neutral. The charge of one proton is equal in strength to the charge of one electron. When the number of protons in an atom equals the number of electrons, the atom itself has no overall charge, it is neutral. ELECTRONS CAN MOVE The protons and neutrons in the nucleus are held together very tightly. Normally the nucleus does not change. But some of the outer electrons are held very loosely. They can move from one atom to another. An atom that looses electrons has more positive charges (protons) than negative charges (electrons). It is positively charged. An atom that gains electrons has more negative than positive particles. It has a negative charge. A charged atom is called an "ion." Some materials hold their electrons very tightly. Electrons do not move through them very well. These things are called insulators. Plastic, cloth, glass and dry air are good insulators. Other materials have some loosely held electrons, which move through them very easily. These are called conductors. Most metals are good conductors. How can we move electrons from one place to another? One very common way is to rub two objects together. If they are made of different materials, and are both insulators, electrons may be transferred (or moved) from one to the other. The more rubbing, the more electrons move, and the larger the charges built up. (Scientists believe that it is not the rubbing or friction that causes electrons to move. It is simply the contact between two different materials. Rubbing just increases the contact area between them.)

3 Static electricity is the imbalance of positive and negative charges. OPPOSITES ATTRACT Now, positive and negative charges behave in interesting ways. Did you ever hear the saying that opposites attract? Well, it's true. Two things with opposite, or different charges (a positive and a negative) will attract, or pull towards each other. Things with the same charge (two positives or two negatives) will repel, or push away from each other. A charged object will also attract something that is neutral. Think about how you can make a balloon stick to the wall. If you charge a balloon by rubbing it on your hair, it picks up extra electrons and has a negative charge. Holding it near a neutral object will make the charges in that object move. If it is a conductor, many electrons move easily to the other side, as far from the balloon as possible. If it is an insulator, the electrons in the atoms and molecules can only move very slightly to one side, away from the balloon. In either case, there are more positive charges closer to the negative balloon. Opposites attract. The balloon sticks. (At least until the electrons on the balloon slowly leak off.) It works the same way for neutral and positively charged objects.

4 BASIC ELECTRONIC CIRCUITS EXPLAINED In this section we will discuss what a circuit is Circuit A circuit is a path for electrons to flow through. The path is from a power sources negative terminal, through the various components and on to the positive terminal. Think of it as a circle. The paths may split off here and there but they always form a line from the negative to positive. NOTE: Negatively charged electrons in a conductor are attracted to the positive side of the power source. Conductor A conductor is a material (usually a metal such as copper) that allows electrical current to pass easily through. The current is made up of electrons. This is opposed to an insulator which prevents the flow of electricity through it.

5 Simple Circuit If we break a circuit down to it's elementary blocks we get: 1) A Power Source -- eg: battery 2) A Path -- eg: a wire 3) A Load -- eg: a lamp 4) A Control -- eg: switch (Optional) 5) An indicator -- eg: Meter (Optional) Series Circuit A series circuit is one with all the loads in a row. Like links in a chain. There is only ONE path for the electricity to flow. If this circuit was a string of light bulbs, and one blew out, the remaining bulbs would turn off. NOTE: The squiggly lines in the diagram are the symbol for Resistors. The parallel lines are the symbol for a battery. Parallel Circuit A parallel circuit is one that has two or more paths for the electricity to flow. In other words, the loads are parallel to each other. If the loads in this circuit were light bulbs and one blew out there is still current flowing to the others as they are still in a direct path from the negative to positive terminals of the battery. There are specific properties to a parallel circuit that will be described in another section.

6 Combination Circuit A combination circuit is one that has a "combination" of series and parallel paths for the electricity to flow. Its properties are a synthesis of the two. In this example, the parallel section of the circuit is like a subcircuit and actually is part of an over-all series circuit.

7 VOLTAGE, CURRENT & RESISTANCE EXPLAINED In electronics we are dealing with voltage, current and resistance in circuits. In the next section we'll learn that by using Ohm's Law we can determine one value by knowing the other two (For example: Figure out Current by using Voltage and Resistance values). So it is important to firmly grasp the basics of Voltage/Current/Resistance first. We will describe these electrical terms using an analogy that closely resembles electronics HYDRAULICS. Voltage Voltage is the electrical force, or "pressure", that causes current to flow in a circuit. It is measured in VOLTS (V or E). Take a look at the diagram. Voltage would be the force that is pushing the water (electrons) forward.

8 Current Current is the movement of electrical charge - the flow of electrons through the electronic circuit. Current is measured in AMPERES (AMPS, A or I). Current would be the flow of water moving through the tube (wire). Resistance Resistance is anything that causes an opposition to the flow of electricity in a circuit. It is used to control the amount of voltage and/or amperage in a circuit. Everything in the circuit causes a resistance (even wire). It is measured in OHMS ( ).

9 Ohm s Law is a set of formulas used in electronics to calculate an unknown amount of current, voltage or resistance. It was named after the German physicist Georg Simon Ohm. Born Died TECHNICAL DEFINITION ALERT! Ohm's Law is a formulation of the relationship of voltage, current, and resistance, expressed as: Where: V is the Voltage measured in volts I is the Current measured in amperes R is the resistance measured in Ohms Therefore: Volts = Amps times Resistance Ohms Law is used to calculate a missing value in a circuit.

10 MULTIMETER ULTRA BASICS A handheld multimeter is the most important tool you will use in electronics. You will use it to determine voltage/amperage/resistance in a circuit, learn the relationship of V, I (amperage) & R to each other, troubleshoot, test circuits and countless other tasks. FEATURES Here are the features you will need or should look for in a meter: 1) It should measure: a. AC Voltage b. DC voltage c. Amperage d. Resistance e. Capacitance - Some do not have this. If so, find one that does or buy a capacitance meter separate. Don't try to convince yourself you do not need this feature. 2) Continuity Checker with audible beep. 3) Diode Checker with audible beep. 4) Optional but HIGHLY recommended is a frequency counter. 5) Try to get a meter with auto ranging and not one that you have to keep turning a dial (or pushing a button) to shift to different ranges. There is nothing more annoying then having to take your hands away from the probes to change from 300mV to +10Vs. 6) Make some alligator clips for the probe tips. My Fluke didn't come with them but I just bought a few push-on ones later.

11 NAME SECTION Electricity Review *List the three particles and their charges that make up an atom. Particle Charge *What is electricity? *What is a conductor? *What is an insulator? *Describe who the valence ring determines what type of material is produced by the number of electrons in it. *List six ways that we move electrons (EMF) *Draw an atom.

13 Draw a circuit that can turn two lights on and off alternately (when one is on the other should turn off) using only one switch. Draw an example of a series and parallel circuit. What is the difference between a battery and a cell? What does AC and DC stand for? Where does electricity want to go? 12 Volts 2 Ohms Amps I=20 R=2 E= V 10 A R 100 A 10 R V 5 A 25 V R 10 R 100 V A ACROSS 2 Particles that have no charge 4 Allows electricity to flow through it freely 6 Fuses and protect electrical circuits and devices 9 The "A" in AC 10 Measures electric pressure or force 12 Electricity wants to travel to here 16 Resists the flow of electricity 17 Electricity travels at the speed of (186,000miles/sec.) 19 The center of the atom 20 Measures the current of flow through a circuit 21 Multiple cells hooked up together DOWN 1 Particles that have a positive charge 3 Particles that have a negative charge 5 The "D" in DC 7 Lightning is a form of of this type of EMF 8 Moving electrons 11 Most common form of EMF 13 The outer electron ring of an atom 14 The light should be on in this type of circuit 15 Measure the resistance in a circuit 18 A side effect of resistance

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